1. Field of the Invention
The present invention relates to an electronic circuit package having a circuit substrate on which an electronic circuit is formed, such as an ignition control circuit for an internal combustion engine, and a case for accommodating the circuit substrate.
2. Description of the Related Art
FIG. 5 is a plan view showing an example of a conventional electronic circuit package; and FIG. 6 is a cross-sectional view taken along the line VI--VI of FIG. 5. In the figures, a connector unit 1a for external connection and a substrate accommodating chamber 1b are formed in a case 1 made of resin. A circuit substrate 2 is fixed onto a bottom surface 1c of the substrate accommodating chamber 1b. An electronic circuit (not shown) is formed on the circuit substrate 2, and a plurality of electronic components (not shown) are mounted thereon.
A plurality of terminals 3 are integrally formed so as to be fixed in the case 1. The respective terminals 3 each comprise an external connecting portion 3a located in the connector unit 1a and an internal connecting portion 3b located in the substrate accommodating chamber 1b. The internal connecting portions 3b are formed by bending the end portions of the terminal 3 so that they extend perpendicular with respect to the bottom surface 1c of the substrate accommodating chamber 1b and the substrate 2.
The electronic circuit formed on the circuit substrate 2 is electrically connected to the terminals 3 by a plurality of leads 4. The respective leads 4 each include a first end portion 4a soldered on the circuit substrate 2 and a second end portion 4b welded to the internal connecting portion 3b of the terminal 3.
With such an arrangement of the electronic circuit package, after the circuit substrate 2, with the leads 4 soldered thereon, has been fixed in the interior of the substrate accommodating chamber 1b, the second end portions 4b of the leads 4 are resistance welded to the internal connecting portions 3b of the terminals 3. By employing the above method in which the leads 4 are connected to the terminals 3 by means of resistance welding, not soldering, the strength of the connecting portion becomes stable, which makes it possible to improve reliability, as well as perform assembly with simple equipment.
FIG. 7 is a cross-sectional view showing another example of a conventional electronic circuit package. This example shows that a circuit substrate 2 is coated with a resin 5 and a substrate accommodating chamber 1b is sealed by a cover 6. With such an arrangement in which the circuit substrate 2 is coated with the resin 5, it is possible to prevent welding chips, generated when leads 4 are resistance-welded to terminals 3, from flying onto the circuit substrate 2 and short circuiting the electronic circuit. The cover 6 is attached to the top of the case 1 after the above-mentioned resistance welding.
FIG. 8 is a cross-sectional view showing still another example of a conventional electronic circuit package. In this example, a circuit substrate 2 is coated with a resin 5, leads 4 are resistance-welded to terminals 3, and then a resin 7 is changed into a substrate accommodating chamber 1b.
With the conventional electronic circuit packages having the above arrangements, since inner connecting portions 3b of the terminals 3 extend in a direction perpendicular to the substrate 2 and the welding portions are located above the circuit substrate 2, there is a fear that welding chips will fly onto the circuit substrate 2. Also, in order to avoid short circuits caused by flying welding chips, the circuit substrate 2 must be coated with the resin 5. Consequently, corresponding equipment and/or processes are required.
Further, conventionally, the leads 4 must be welded to the terminals 3 above the surface of the protective resin 5. Additionally, in order to prevent welding failure due to the resin 5 adhering to the welding surface, some clearance is required between the welded portions and the upper surface of the resin 5. Therefore, the height (thickness) of the package, that is, the vertical direction shown in FIG. 6 will be of a larger dimension. Such a large height dimension of the package requires a large amount of resin 7 to fill the package, as illustrated in FIG. 8, resulting in increased costs.